Message-ID: <4777BDA5.4050203@keyaccess.nl>
Date: Sun, 30 Dec 2007 16:47:49 +0100
From: Rene Herman <rene.herman@keyaccess.nl>
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To: Ingo Molnar <mingo@elte.hu>
CC: Alan Cox <alan@lxorguk.ukuu.org.uk>,
       Linus Torvalds <torvalds@linux-foundation.org>, dpreed@reed.com,
       Islam Amer <pharon@gmail.com>, hpa@zytor.com,
       Pavel Machek <pavel@ucw.cz>, Ingo Molnar <mingo@redhat.com>,
       Andi Kleen <andi@firstfloor.org>, Thomas Gleixner <tglx@linutronix.de>,
       Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] x86: provide a DMI based port 0x80 I/O delay override
References: <477711DC.5030800@keyaccess.nl> <alpine.LFD.1.00.0712300124440.32517@woody.linux-foundation.org> <20071230144700.78f4605c@the-village.bc.nu> <20071230152835.GX16946@elte.hu>
In-Reply-To: <20071230152835.GX16946@elte.hu>
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On 30-12-07 16:28, Ingo Molnar wrote:

> Reading from the 0x3cc port does not impact the cursor position update 
> sequence IIRC - i think the vidport is even ignored for the input 
> direction by most hardware, there's a separate input register. The 0x3cc 
> port is a well-defined VGA register which should be unused on non-VGA 
> hardware. (which makes it a perfect delay register in any case)

Hardly. Duron 1300 on AMD756:

rene@7ixe4:~/src/port80$ su -c ./port80
cycles: out 2400, in 2401
rene@7ixe4:~/src/port80$ su -c ./port3cc
cycles: out 459, in 394

As stated a few dozen times by now already, port 0x80 is _decidedly_ _non_ 
_random_

Rene.

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